1. Field of the Invention
This invention relates generally to web winders and rewinders and specifically to an improved web cutting and transfer mechanism for turret-type web winders.
2. Description of Related Art
In the processing of materials such as paper, film, foil, and the like, a web of the material is often provided from a series of supply rolls. The web is unwound from the rolls, processed, and rewound to form several finished rolls. The rewinder is preferably constructed to maintain continuous, uninterrupted winding of the new rolls. A series of rollers are arranged to move the web to desired processing locations and guide the web to a core on which it is rewound.
The rewinder includes a cutoff and transfer mechanism for automatically cutting the web and transferring the web from the end of a full roll to a new core to form the next roll. Many arrangements are known for indexing the rolls and positioning the web so that the web can be transferred to a new core and a full roll can be removed without interrupting the rewinding. Typically, cores on which the rolls are formed are mounted on a rotatable turret. The turret is rotated to position a new core adjacent a transfer mechanism. Transfer mechanisms typically include a serrated blade which is driven into the web. Other mechanisms provide a means to move the web into the blade to cut the web. In either case, the leading edge of the cut web is guided onto the new core to begin a new roll. An adhesive, such as tape, is often provided on the core to secure the leading edge.
Preferably, the leading edge of the web is placed on the core in a smooth and even fashion. Thus, the leading edge should be cut smoothly and should not fold back on itself. If an adhesive is used on the core, it should not form a lump in the roll. Because the cores are often reused many times, the cores should not be damaged by the rewinding, and residue from the adhesive should not be left on the cores.
Winders which transfer the web onto the new core by deflecting the web into a stationary blade have been described in several patents.
U.S. Pat. No. 3,086,725 to Zernov shows a turret winder having a blade on movable, elongated arms located near a new core on which a web is to be wound. The core is provided with adhesive such as an adhesive tape. A presser roller and a guide bar are located on the opposite side of the web from the blade. A pair of arms move the guide bar and roller into the blade to cut the web and press the web onto the core.
U.S. Pat. No. 4,326,680 to Tetro et al shows a winder having a blade on a movable arm. A curved guide conforming to a new core forms a part of the arm holding the blade. Prior to cutting, the web is moved into position against the core by an enveloper roller on movable arms. A movable deflector is mounted on the arms with the enveloper roller. The deflector is moved into the web to cut the web on the blade. The guide physically guides the leading edge of the web around the core.
U.S. Pat. No. 4,326,679 to Phelps et al shows a winder having a blade on a movable arm. A curved guide conforming to a new core forms a part of the arm holding the blade. Prior to cutting, the web is moved into position against the core by a pressure roller on movable arms. A movable deflector including a curved guide is mounted on another set of movable arms. The deflector is moved into the web to cut the web on the blade. The guides physically guide the leading edge of the web around the core.
Instead of using a deflector, U.S. Pat. No. 4,422,586 to Tetro uses a pressure roller to press the web against the new core prior to cutting. The core is provided with an adhesive so that the web is pulled into a blade by the core. It is suggested that a brush or an air jet could be used instead of the pressure roller. As can be seen in Tetro '586 the blade will tend to peel the web from the core, especially at high speeds, thus, the adhesive must be very strong. The adhesive typically used has an adhesion to steel on the order of 45 lbs./in., such as 3M Company's No. 910 splicing tape. Peeling and bending of the web may cause it to slide over the blade thereby making a rough cut which causes an uneven application to the core and creates dust from the web and its coating. To ensure sufficient bonding with the web and efficient cutting, the knife must be positioned close to the core, therefore the core cannot be eccentric. When the web is relatively thick, it may be pulled from the core before it is cut by the blade.
Several patents show winders in which a blade is moved into the web and an air jet is used to push the web onto the core. U.S. Pat. No. 4,919,352 to Terp et al shows an air jet emanating from an elongated arm. U.S. Pat. No. 4,529,141 to McClenathan shows the air emanating from part of a vacuum type roller. U.S. Pat. No. 3,592,403 to Schmitt et al shows air emanating from a pressure roller. In each of these references the air is directed toward the core at an angle to push the web onto the core. U.S. Pat. No. 3,889,892 to Melead merely suggests that an air jet could be used. It has been found that, because a blade assembly is relatively bulky and must be moved quickly, it is preferable for the blade to remain stationary during cutting. Moreover, air jets directed at the web can have the undesirable effect of pulling the web away from the core according to the Bernoulli Principle. The faster moving air from the air jet has a lower lateral pressure than the stationary air between the web and core.
In all of the prior art references, air between the web and the core tends to inhibit motion of the web toward the core. In addition, the flexible web is pushed onto the new core with an air jet or merely by the continuing motion of the web. When pushing a flexible member, it is difficult to control the leading edge, thus, as shown in some of the references, a mechanical guide is used. However, such a guide creates friction with the web and may cause the web to fold back on itself or may damage the leading edge thereby creating dust.
Accordingly, it would be desirable to have an improved web transfer mechanism in which the blade is stationary when the web is cut. The web should be cut cleanly without creating dust or a ragged edge. The web should be pulled onto the core without the friction incident to a mechanical guide. The mechanism should urge the web onto the new core and evacuate air from between the web and the core. The web should lay on the core without folding back or having a lump of adhesive tape.